title: Achilles tendon vibration shifts the center of pressure backward in standing and forward in sitting in young subjects.
abstract: OBJECTIVE
  An Achilles tendon (AT) vibration is known to disrupt the postural control in standing ("vibration-induced falling", VIF) and to backward tilt the postural vertical in restrained sitting position, suggesting a link between AT vibration and internal representations involved in postural control. A recalibration of some troubles in body orientation by oriented sensory manipulations could be of great clinical interest. In order to use the VIF paradigm in a procedure suitable for a rehabilitation context, AT vibration deserves to be more investigated in sitting, for security reasons, and first in young participants.
  
  
  METHODS
  In 12 healthy participants (6 men/6 women; 23.3±1.9 years), posturographic data to AT vibrations (85 Hz) were recorded over 30 s standing and 40 s sitting trials.
  
  
  RESULTS
  Surprisingly, four types of differences were found between standing and sitting AT vibrations: presence/absence of VIF and kinesthetic illusion, opposite directions of the centre of foot pressure (CoP) displacements, different temporal profiles. In standing: VIF without kinesthetic illusion, rapid backward shift of CoP with a peak of -54.6±11.3 mm (with respect to baseline P<0.001) 2.8±0.2 s after vibration onset. In sitting: surprising systematic forward shift of the CoP throughout the duration of AT vibration with a maximum of 27.9±18.9 mm (P<0.05 with respect to the baseline) 19.6±0.3 s after vibration onset, associated with a kinesthetic illusion in most subjects.
  
  
  CONCLUSIONS
  The present study invalidates our idea to extend in sitting the VIF paradigm but the unexpected results open a new window about the basic mechanisms underlying muscle vibration effects.
authors.affiliation: Équipe Santé-Plasticité-Motricité, Laboratoire TIMC-IMAG, UMR UJF CNRS 5525, Université Grenoble 1, 38041 Grenoble, France. Electronic address: guillaume.barbieri@imag.fr.
authors.forename: G
authors.initials: G
authors.lastname: Barbieri
authors.forename: A-S
authors.initials: AS
authors.lastname: Gissot
authors.forename: V
authors.initials: V
authors.lastname: Nougier
authors.forename: D
authors.initials: D
authors.lastname: Pérennou
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D004856:Postural Balance / Q000502:physiology*; D011312:Pressure; D055815:Young Adult
keywords: Contrôle postural; Force platform; Plateforme de force; Postural control; Proprioception; Verticality; Verticalité; Vibration